This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Adaptive streaming over HTTP (also called multi-bitrate switching) is quickly becoming a major technology for multimedia content distribution. Among the HTTP adaptive streaming protocols which are already used, the most famous are the HTTP Live Streaming (HLS) from Apple, the Silverlight Smooth Streaming (SSS) from Microsoft, the Adobe Dynamic Streaming (ADS) from Adobe and the Dynamic Adaptive Streaming over HTTP (DASH) developped by 3GPP within the SA4 group.
When a client terminal wishes to play an audiovisual content (or A/V content) in adaptive streaming, it first has to get a file describing how this A/V content might be obtained. This is generally done through the HTTP protocol by getting a descripting file, so-called manifest, from an URL (Uniform Resource Locator), but can be also achieved by other means (e.g. broadcast, e-mail, SMS and so on). The manifest basically lists the available representations (also called instances or versions) of such an A/V content (in terms of bitrate, resolution and other properties); one representation per quality level (bitrate). Each representation is made of a series of chunks of equal duration—accessible by a separate URL—and has a set of descriptive elements attached for selection by the client. Said manifest is generated in advance and delivered to the client terminal by, for instance, a remote server.
Indeed, the stream of data corresponding to the A/V content is available on an HTTP server with different qualities. The highest quality is associated with a high bitrate; the lowest quality is associated with a low bitrate. This allows distribution to many different terminals which might be subject to highly varying network conditions.
The whole data stream of each representation is divided into chunks of equal duration which are made such that a client terminal may smoothly switch from one quality level to another between two chunks. As a result, the video quality may vary while playing but rarely suffers from interruptions (also called freezes).
At the client side, the chunks are selected based on a measure of the available bandwidth of the transmission path. In particular, a client terminal usually requests the representation of a chunk corresponding to a bitrate encoding and thus a quality compliant with the measured bandwidth.
When a cache is along the transmission path between a client terminal and a remote server which frequently occurs, one representation of a given chunk may already be stored in said cache, in case another client has previously requested the same chunk with the same representation or in case a Content Delivery Network (CDN) has already provisioned the chunk in the cache. Thus, the response to an HTTP request for said given chunk is faster than if the chunk comes from the remote server and duplicate transmission can be avoided, effectively saving network resources.
Nevertheless, the HTTP adaptive streaming appears not to be cache friendly (or at least less cache friendly than the so called layered base switching as for instance H264-SVC). Indeed, if a first client terminal requests a representation r of a given chunk and a second client terminal—sharing a part of the transmission path with said first client terminal and a cache—requests a representation r′ of said given chunk (at a higher or lower quality), then the cache is not hit leading to higher load on the network segment between the cache and the server with the risk of causing congestion. The benefits of caching are then completely annihilated and caches are currently unable to improve this situation.
The present invention focuses on preventing network congestions and, in particular, attempts to operate caches possibly located along the transmission path between a client terminal and one or several remote servers.